The present invention relates to bearings for high-speed rotors, in particular for turbo-superchargers including two bearing supports arranged in an axially spaced relation, each having an axial and a radial bearing surface, and a bearing bush non-rotatively maintained and supported on the bearing body by means of external damping surfaces.
In connection with the design of bearings for high-speed rotors, the designers are facing most exacting demands due to a variety of functional, constructional and operational requirements partly contradicting one another. From an operational viewpoint, problems affecting the bearing power loss and bearing stability are of considerable import for the design of similar bearings. With bearings of similar geometrical design features, the bearing power loss is known to be approximately proportionate to the fifth power of the bearing diameter. It accounts for a substantial share of the turbine performance, particularly with small-size turbo-superchargers such as for passenger car and truck engines. Particularly in the low-speed range of the engines, this is apt to have an extremely adverse effect upon the torque and throttle response of the supercharged engines. In addition to the energy dissipated by direct bearing friction, energy is also lost by lubricating oil spattered from members of the rotor, i.e., due to the braking action of such amounts of lubricating oil as are splashed back to the rotor elements. Experience shows that such losses have been comparatively large with conventional bearings for high-speed engines.
However, these shares of losses should be kept as low as possible while at the same time assuring also an adequate stability of the bearings. In order to keep the bearing diameters, and, consequently, the power losses of the bearings, on a low level, in most cases only the third critical speed of rotation of the rotor is higher than the maximum operational speed. At any rate, the bearing strength and the damping power of the bearings inclusive of the external damping of the bearing bush have to be high enough to prevent the build-up of rotor oscillations with the areas of the first and second critical speed of rotation. Only under these circumstances, is it possible to dispense with the customary fine oil filtering and the considerable expense involved.
As regards the structural sizes and structural weights of the turbo-chargers, there are generally certain natural limitations imposed thereupon by considerations of engine design, as a result of which the freedom of bearing design is further restricted.
However, with regard to production technique, the designer has to meet ever increasing demands. This is further due to the fact that in view of rapidly expanding legislation in the field of environmental protection, the use of turbo-superchargers for the supercharging of truck engines is constantly increasing. As a result, the energy crisis is bound to lead to a large extent to ever smaller supercharged low-loss engines both for trucks and passenger vehicles and for other types of driving mechanisms. Consequently, future mass production trends will show a tendency towards even minor savings which will produce economical results of decisive importance.